In our information-driven society, math ability is essential for success, particularly in the STEM fields that drive the modern economy. Within the population, however, there exist large variations with regard to math ability, and this variabilityis already present in the first year of formal schooling. Furthermore, math ability in kindergarten is a strong predictor of a child's later academic and professional achievement. Many interventions have focused on executive functions (EFs) and early number knowledge as routes to improve preschool-aged children's math proficiency, though they have been met with mixed success. However, reasoning ability, which is critical for flexible problem solving and correlates strongly with math ability, has received relatively little focus despite the possibility that improving reasoning ability in young children may be a promising route to impacting later math performance. The NICHD strives to develop more personalized and effective cognitive interventions. In line this with this goal, the specific objective of this application is to identiy the cognitive skills and neural substrates that support the link between reasoning and math. Aim 1 will test the causal role of specific cognitive skill sets in the growth of math achievement. Preschool-aged children will receive game- based interventions that target either reasoning ability or EFs. The hypothesis is that growth in reasoning will lead to improvements in children's ability to recognize ordinal relations between numerical magnitudes, which will result in greater improvements in arithmetic performance relative to the EF-focused intervention. Pupillometry metrics during a reasoning task will be used to investigate the temporal dynamics of children's ordinal reasoning, providing insight into the mechanisms of change promoted by the interventions. Aim 2 will characterize the links between reasoning ability, math achievement, and brain function in children aged 6-19 years. This aim takes advantage of a preexisting longitudinal dataset investigating the neural and cognitive factors that support reasoning development. The NIMH aims to understand the neural bases of complex behaviors. The hypothesis is that growth in math performance will be related to changes in functional activity and connectivity within the fronto-parietal brain networks implicated in reasoning development. Together, these data will tell us which targets of intervention are most effective at improving children's math performance and will provide insight into the neural changes that support growth in math performance. This approach is innovative it its multimodal methodology, because it combines methods from developmental psychology, cognitive psychology, and cognitive neuroscience in order to improve our understanding of the factors that promote growth in math ability. The proposed research is significant because understanding the connection between reasoning and math is critical for the development of novel assessments of math ability and educational interventions to promote growth in math, both of which are necessary to improve school readiness and academic performance in young children.